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9th International Congress of the Brazilian Geophysical Society
- Conference date: 11 Sep 2005 - 14 Sep 2005
- Location: Salvador, Bahia, Brazil
- Published: 11 September 2005
121 - 140 of 462 results
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Finite difference modeling of 2D GPR data considering attenuation
Authors M. Heimer, M.A. Barsottelli Botelho and S. Pomponet OliveiraWe use a finite-difference scheme to simulate 2D ground penetrating radar data by solving the damped wave equation. We show that the stability condition for the damped scalar wave equation does not depend on the damping factor. As an example application of our modeling tool we investigate a typical situation in granite prospecting, where a conductive clay overburden masks the real position of the fractures in the granite. The results of the modeling have a good agreement with the actual data. Also, the algorithm shows well the increase in attenuation with the increase of the frequency. The algorithm shows to be a good basic modeling tool that can be used for further applications and for comparisons with other modeling methods like pseudospectral or finite elements.
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Utilização do GPR 3D bi-polarizado na localização de um BOP soterrado devido a colapso de terreno no Campo de Fazenda Belém, Bacia Potiguar
Authors P.X. Neto and W.E. de MedeirosO GPR utiliza antenas para irradiar a energia eletromagnética para o meio geológico. Esta energia, ao se propagar no meio geológico, sofre reflexão quando encontra interfaces com contrastes de impedância eletromagnética (interface litológica, objetos enterrados, etc) e é recebida pela antena receptora. A energia refletida por um alvo é função da amplitude e da direção de vibração (polarização) do campo eletromagnético incidente. Isso implica que o receptor é sensível à direção de vibração do campo eletromagnético e, portanto, sensível à morfologia ou disposição espacial do alvo.
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Interpretação em 3D de Dados de GPR em Estação de Interpretação de Dados Sísmicos
Authors A.J. Pereira, L.A.P. Gambôa, M.A.M. da Silva, A.R. Rodrigues and A. da CostaCom a conversão dos dados de GPR adquiridos em formato próprio, para um formato seg-y genérico passível de carregamento em estação de interpretação sísmica, foi possível a visualização em 3D de feições representativas da estratigrafia de um trecho da praia de Itaipuaçú, município de Maricá, Estado do Rio de Janeiro. Essa possibilidade permitiu a identificação nos perfis de feições correspondentes a canais que alimentavam uma paleolaguna, hoje colmatada, no reverso do cordão arenoso externo, além de estruturas análogas às feições observadas atualmente no pós-praia da referida praia, como por exemplo paleoescarpas de tempestades. Outra constatação foi verificar, ao longo de toda a planície mapeada, o lençol freático que ocorre em torno de 5 m de profundidade.
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Monitoramento da umidade de campo empregando a técnica de radar GPR
Authors N.S. Amparo, S.L. Machado, T.C. Dourado and M.A.B. BotelhoThis paper intends to evaluate the GPR potential of use aimed to obtention of water contente profiles in the vadose zone. In order to do that, a laboratory mechanical apparatus was developed in way that constant mid point tests can be perfomed, allowing the obtention of precise CMP radagrams. The apparatus, a sand box wit nominal dimensions of 1 x 0,7 x 0,7 m, had a mechanical device that assures equal displacements from central point. Laboratory tests were performed in order to calibrate equipament and obtain experimental data correlating soil water content and pulse travel velocities theoretical equation, develop inside the scope of the research program, was used in order to predict the relative amounts of water and air in the soil voids.
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Towards cost-effective 3D imaging with GPR
More LessThere are two situations that can motivate a GPR user to perform the investigation in a 3D mode rather than in the conventional 2D mode. The first case is when the 2D approach is not enough to achieve a reliable answer to a specific problem while 3D imaging has the potential for solving the problem correctly.
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Experimentos em Laboratório (1 GHz) e Trabalhos de Campo (200 MHz) com GPR Usando Corpos arenosos para Avaliar a Influência da água e de Hidrocarbonetos na Velocidade e na Amplitude da Onda Eletromagnética
Authors T.C. Dourado, M.A. Barsottelli Botelho, S.L. Machado and N.S. AmparoWe analyse GPR measurements (1 GHz) which were carried out on a well sorted, clean sand in a laboratory experimental site and we also executed AVO field experiments, both using TE and TM- mode configurations,. The AVO works were conducted on a sand dune field around the Lagoa do Abaeté (Salvador, Brazil).
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Detecting cavities and archaeological remains with GPR
Authors E.U. Ulugergerli and S. KadiogluTwo examples were considered in this presentation; detection of cavities in limestone, delineation of boundaries of an archeological remain using Ground Penetrating Radar (GPR) method and affect of the trees on the GPR data. The GPR method has been successfully applied to detect and map underground cavities in Limestone in a reservoir area of a dam being built in southeast Turkey.
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Multi-offset GPR surveys for complex targets
Authors L. Baradello, J.M. Carcione and D. Nieto YabarDuring the last twenty years Ground Penetrating Radar (GPR, georadar) has been successfully used to discover and map several subsurface structures. The mono-static georadar (one single antenna) is fast and inexpensive for these surveys. Often, in archaeological and geological investigations the structures can be very complex: ancient walls and debris in chaotic mixtures of sediments or fractures in rocks. These cases are difficult to interpret with conventional single-offset (SO) records because there is scattering and poor signal-to-noise (SN) ratio. The present paper shows how the GPR multi-offset (MO) technique can provide more information about complex targets and enhance weak reflections. We compare the multi-fold (MF) stack and the MO section to investigate which method gives the best performance.
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Imaging an hyperpicnal turbidite outcrop in Almada Basin (Brazil)
Authors M.A.R. Ceia, A.A.G. Carrasquilla and J.M. TravassosIn onshore Almada Basin, northeast Brazil, sandy and/or conglomeratic turbidites and shales outcrops of Urucutuca Formation occur. These rocks are part of an exhumed portion of the filling-section of the Almada Canyon, which is well mapped by seismic studies in offshore part.
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GPR simulations for pipeline oil drainage detection
Authors M.A.R. Ceia and A.A.G. CarrasquillaPipeline detection and investigation of leakage and fluid drainage play a major part in geophysics applied to downstream problems. Oil drainage may have impact in contaminating subsurface environment, and by consequence, affect socially and economically the nearby population. When that hazard occurs, it could be mapped by geophysical techniques. The strong contrast in electrical properties between oil (or gas), metallic pipes and sediments, makes GPR (ground penetrating radar) one of the best techniques to be used for mapping oil drainage and for pipeline detection.
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Estratigrafia de Alta Resolução da Formação Coqueiro Seco (Bacia de Sergipe-Alagoas) Através da Interpretação de Dados GPR
Authors P.T.L. Menezes, J.M. Travassos and L.S. FrancoA major problem related to carbonates reservoirs is the heterogeneity of porosity and permeability systems. Reservoir analogues can provide valuable definitions of geometric and petrophysical heterogeneities at inter well scales. Integration of ground-penetrating radar (GPR) surveys with sedimentological and stratigraphic data provides information on the internal heterogeneities of sedimentary sequences.
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GPR aplicado ao estudo de Reservatórios Análogos. Estudo de caso em Cordões Litorâneos do Delta do Rio Itapemirim (ES), Resultados Preliminares
Authors G.M. Sousa, P.T.L..J.C. Della Fávera and M.A.M. MedeirosClastic reservoirs analogues based on the interpretation of GPR data provide valuable definitions of geometric and petrophysical heterogeneities of sedimentary sequences at scales that allow dissection of the 3-D anatomy of clastic depositional systems.
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Discussão do conceito de Skin Depth e estimativa de parâmetros elétricos considerando os efeitos de polarização envolvidos a partir de medidas com GPR
The authors analyze, in this work, the polemic question of the signal, being measured by GPR, coming from depth greater than the plane wave skin depth. They conclude that signals are being measured, reflected from depths of the order of five times the skin depth for the 100 MHz frequency being used. They also estimate the dielectric constant for the mapped geologic formations using GPR.
More realistic values of K are obtained, for considering: a) the squared index of refraction, (c/v)2, as due to the electronic polarization, associated to the rock matrix, KM; b) the orientational polarization for the saline water, equal to 78, being considered for the water saturated pore spaces of the rocks, Kf. The mixed relation for a two components material was then used for the finalestimation.
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Aquisição e Processamento em Dados de Ground-Penetrating Radar (GPR) COS e Split-Spread
More LessAquisições de dados de GPR common offset (COS) (monocanal) e split spread (multicanal), com antena de 100 MHz foram realizadas em um afloramento com uma seção geológica que é marcada por variações estruturais na forma de um graben. Os dados de radar foram processados com o pacote Vista 2D/3D seguindo um fluxo de processamento de pré-empilhamento com edição dos dados, correção estática, escalonamento, filtro variável com o tempo, análise de velocidade, correção NMO, mute, e pós-empilhamento com escalonamento, filtro variável com o tempo, filtro multi-canal e migração. As seções finais são apresentadas em profundidade com os dados split-spread fornecendo uma maior representação das feições estruturais e litológicas do afloramento em comparação aos dados COS. A análise das técnicas de processamento de dados sísmicos para os dados de GPR em afloramentos vem a colaborar para o estudo de reservatórios em grandes profundidades, auxiliando em ajuste de parâmetros e verificando a eficácia dos processamentos sísmicos.
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Emprego do GPR para a Caracterização da Morfologia do Fundo e Espessura dos Depósitos da Represa de Guarapiranga, São Paulo / SP
Authors Renato Hochgreb Frazão, Jorge Luís Porsani and Renato Luiz PradoGuarapiranga reservoir is one of most important raw water reservoir for the city of São Paulo locate in an area of high population density in SE Brazil. It is responsible for 20% of potable distribution water. During the last decades the reservoir is experiencing a growing eutrophication process due to untreated sewage discharge. Preliminaries Ground Penetrating Radar (GPR) investigations were carried out in area of Guarapiranga reservoir by determine water depth and perform sub-bottom sediment profiling. Accurate periodic information on the elevations the top of sediment and top of original reservoir bottom is important to calculate the volume of sediment to be removed and to establish the reference elevations for the proposed dredging activities. The measurements are non-intrusive and non-destructive, and were conducted along survey lines. Compared with other geophysical methods, GPR profiles have a very high resolution. The selection of the optimum radar frequency is essential to obtain a good resolution and sufficient depth penetration. The obtained results are very interesting.
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Geologia Estrutural da Bacia Potiguar com base em dados aeromagnéticos
Authors Marcos de Barros Munis and Renato Lopes SilveiraThe E&P Data Bank - BDEP - is the trustee depositary of all geophysical project concerned with E&P activities in Brazil. Especulative data and proprietary data has a confidentially term of 10 or 5 years, respectively. After that, they became public and can be acquired by companies, universities, and others interested by a small price, aiming the further development of oil prospecting knowledge or either production.These public data are available for all the mineral and oil community in CD media. With the development of softwares on processing and filtering geophysical data, good opportunities are open to all. This paper deals with a fast treatment of aeromagnetic data from Bacia Potiguar, NE Brazil, with an improvement on signal / noise ratio giving new ways on structural geologic interpretations using upward continuation, first derivatives and pole reduced maps.
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Modelagem numérica de dados tensoriais de aerogradiometria gravimétrica 3D
More LessAir-FTG is nowadays the only existing airborne full tensor gradiometer technology that is flown for both detailed and regional surveys. The system takes real-time measurements of the differences in the gravity gradient field in three orthogonal directions and at me time compensates for bias in the orientation and movement of the aircraft. Each one of these measurements is related to either density contrasts or geometry of discrete bodies. In this work we elaborate a numerical algorithm to compute the five synthetic gxx, gxy, gxz, gyy and gyz independent tensor components. Results show that gradiometer depict a more observable advantage for identification of nearsurface targets, revealing structures such as lineaments, edges, corners and as a consequence body hapes and thickness. It is also shown that the best images of the subsurface rocks acquired by the air-FTG platform can provide more realistic information than the conventional vertical ground gravity field instruments when interpreting lateral density contrasts.
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Modelamento do sinal gravimétrico e aeromagnético das Alcalinas de Morro do Engenho, sudoeste de Goiás
Authors Alanna C. Dutra and Yára R. MarangoniA Província Alcalina Rio Verde – Iporá, na borda norte da Bacia do Paraná é caracterizada pela presença de intrusões alcalinas com forte assinatura aeromagnética e gravimétrica, apresentando-se como anomalias quase circulares. O Complexo Morro do Engenho (ME) está ao norte da província e constitui uma intrusão circular zonada de cerca de 5 km de diâmetro em superfície. As anomalias gravimétricas variam de +15 a +30 mGal com relação ao campo gravimétrico regional, enquanto que as anomalias aeromagneticas são da ordem de ±3000nT. O modelamento usando a técnica de inversão indica espessura variando de 10 a 12 km, com circunferência média em torno de 10 km. No modelamento conjunto 2,5D, o sinal aeromagnético parece ser gerado por um corpo de geometria cilíndrica vertical. Este corpo geométrico apresenta-se homogêneo e com profundidade compatível com os modelos gravimétricos.
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Interpretação geológico-geofísica de estruturas continentais e sua continuação em águas rasas na Bacia de Campos, Estado do Rio de Janeiro
More LessThis work presents the preliminary comparative analysis of the regional structures observed in onshore satellite images and their continuation toward the Campos Basin shallow water platform. These results were obtained by integration of aeromagnetic and gravimetric data, satellite images, topographic, and regional structural maps, combined with structural analysis from fieldwork.
The southern portion of the Campos Basin is located over gneissic rocks of the Cabo Frio Tectonic Domain (CFTD), a Cambrian-Ordovician tectonic unit formed during the agglutination of the Gondwana Paleocontinent. All the CFTD lithotypes are tectonically intercalated throughout thrust zones, dipping between 5º and 30º to the south. These units were deformed during D1 and D2 deformation stages, at c.a. 520 Ma (Schmitt et al., 2004). The CFTD was juxtaposed to the tectonic units of the Ribeira Belt during D3 phase. The contact is marked by a thrust fault striking NE-SW that dips 30º to the south, with a vergence towards the NW. This regional structure is present in the Macaé region, from where, supposedly, it inflects in an ENE-WSW direction towards the continental platform, with a predominant NE-SW strike related to Early Cretaceous syn-rift fault trends.
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Interpretação de Dados Aeromagnetométricos na Região do Gráben de São João, Rio<br>de Janeiro, Brasil
More LessSeveral anomaly-enhancement techniques were applied to high-resolution airborne magnetic data of the São João Graben, offshore Cabo Frio platform. That approach allowed the identification of several subtle basement faults and the definition of the tectonic framework.
We idendifiyed new NW-SE faults associated to Early Cretaceous transfer zones that segment the obliquely rifted Atlantic margin. That segmentation has important implications for risk factor of deep-water petroleum systems of Campos Basin.
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